Concrete structures and construction methods

ABSTRACT

Aspects of the invention relate to concrete structures having concrete columns. Cables can provides support as a flat beam in the horizontal slab above so that the columns can be used and largely spanned apart. The columns can be substantially aligned in a row or at least one column can be offset from the row of columns. Further, the concrete structure can include large cantilevered surfaces, such as balconies or walkways. Aspects of the invention further relate to a system for forming concrete columns using tunnel forms. In addition, embodiments of the invention can be used to form an offset column in a secondary pour. Aspects of the invention are particularly well suited for creating multi-level buildings of at least five stories.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application claims the benefit of U.S. Provisional Application No. 60/498,751, filed on Aug. 31, 2003.

FIELD OF THE INVENTION

The invention relates in general to concrete construction and, more particularly, to concrete structures and construction methods using tunnel forms.

BACKGROUND OF THE INVENTION

The use of tunnel forms in construction is known. Generally, tunnel forms are metal structures that can be used to form vertical walls and horizontal slabs simultaneously. The use of tunnels forms in construction provides advantages of speed, reduced construction costs and simplicity. Tunnel forms have proved to be successful, economical and efficient in the construction of buildings that did not require large open spaces such as simple hotels, apartment buildings, and some condominiums.

However, the range of applications in which tunnel forms can be economically and efficiently used is limited because vertical walls must be provided in intervals up to 16 to 18 feet on center to provide support for the horizontal slabs. Such relatively frequent placement of vertical walls can limit the architectural freedom of the building. In situations where more spacing is needed, such as in a parking garage, a transfer slab (a thicker and more expensive horizontal slab) is required the tunnel form building above. Further, tunnel form construction could not be economically applied to the construction of large cantilever surfaces, such as those extending from about 8 feet to about 9 feet. Thus, the use of tunnel forms to construct luxury or premium type buildings was limited. In such buildings, it is desired to have larger rooms or more open spaces, such as about 28 feet by about 28 feet. Again, such constructions are not economical, efficient and simple under current tunnel form construction methods and designs.

Previously, tunnel forms have been used to provide steel columns in a low rise building otherwise made of concrete. These steel columns were in general up to six inches in width. In a limited number of low rise buildings, a post-tensioned flat beam was provided in the horizontal concrete slab over the steel columns, and an upturn beam was used to support the post-tensioned beam. While appropriate for low rise buildings, such a construction is not ideal for taller structures, such as those with five or more stories. Moreover, such a construction can have a number of drawbacks that can diminish the advantages of tunnel form construction.

From a construction standpoint, steel is more difficult to use in forming columns as compared to other materials, such as concrete. Further, the process of forming a steel column within a tunnel form is relatively complicated. For instance, additional labor intensive processes may be required, such as welding two vertically aligned steel columns together. Moreover, the formation of steel columns in tunnel forms is expensive and can significantly increase the cost of a project in comparison to using concrete. Delays can be introduced and the costs can grow significantly when such a construction system is applied to high rise buildings.

In addition, the are a number of limitations in the use of steel columns. When constructing a steel column in a tunnel form, the thickness of the concrete walls of the building dictates the size of the steel columns. Steel columns are limited in strength capacity if a builder wishes to keep the columns the same thickness as the walls of the building or within a reasonable size.

Steel columns are susceptible to corrosion, which can limit the potential areas of use. For instance, it may be desirable to provide open-air parking garages in some buildings, particularly those situated near the ocean. However, a building with steel columns should not be constructed and is not practical near a beach for fear of salt spray corrosion, which can jeopardize the structural integrity of the columns and the building, unless expensive maintenance is applied over the life of the buidling. These concerns may also apply to steel columns located in other open areas of such a building. Further, in the context of a parking garage in a building, use of steel columns is not a standard practice. There are also fire protection issues attendant in steel that are not associated with other materials, such as concrete.

Thus, there remains a need for a construction system and method that minimizes the above concerns and limitations.

SUMMARY OF THE INVENTION

Thus, one object according to aspects of the present invention is to provide a construction system and method for using tunnel forms that can be used economically and efficiently in a variety of buildings, while still maintaining the construction advantages of the tunnel form system. Another object according to the invention is to broaden the range of applications for tunnel forms.

Other objects of the invention relate to using tunnel forms to form concrete columns instead of concrete walls. Further objects of the invention relate to using post-tensioned cables as a flat beam supported by the concrete columns. Still other aspects according to the invention allow the design freedom to have large open areas inside units, combine two or more units together, and/or have large cantilever balconies and walkways, by using a cantilever post-tensioned flat beam formed in the concrete columns or walls. Additional objects relate to minimizing the use of transfer slabs by using flat post-tensioned beams (within the thickness of the slab) spanning over concrete columns. These and other objects according to aspects of the present invention are addressed below.

Aspects of the invention relate to a system and method for using tunnel forms in construction. More particularly, aspects of the invention relate to the application of tunnel form construction to a wide variety of building types while retaining the advantages of tunnel form construction such as speed, relatively low construction costs and simplicity.

In one respect, aspects according to the invention relates to a system and method for using tunnel forms to construct concrete columns instead of solid walls. In a second respect, aspects of the invention relate to spanning the columns as required by the project specification to create the desired open space by supporting the horizontal slab on a post-tensioned flat beam (which can be substantially the same thickness as the slab) spanning between the concrete columns. As a result, aspects of the invention allows for open spaces, such as about 30 feet by about 30 feet, or the construction of large cantilever slab surfaces, such as from about 8 to about 9 feet, by using cantilevered post-tensioned flat beams from the concrete columns or walls, as may be desirable to large create walkways and balconies. Further, aspects of the invention minimize the use of transfer slabs such as over large lobbies or parking garages on the low floors of a building. The minimization or avoidance of the use of transfer slabs, providing large open spaces in the units or between the units, and providing large cantilevered surfaces can be accomplished according to the invention without reducing the benefits provided by the tunnel form construction. In a third respect, aspects of the invention relate to erecting columns that are not within the tunnel wall form because of project specifications or requirements. Such aspects of the invention relate to a secondary concrete pouring operation.

In one respect, embodiments of the invention relate to a method of forming a concrete column. According to the method, a column cage is attached to a dowel set such that the column cage extends substantially vertically upward therefrom. The dowel set can be extend upward from a concrete curb, foundation or column below. A pair of tunnel forms are provided. Each tunnel form has a first wall and a second wall extending substantially perpendicularly therefrom. The tunnel forms are erected such that the second walls of the tunnel forms are substantially vertically oriented and opposingly spaced apart. Thus, the column cage is disposed between the second walls.

First blockouts are positioned in the space between the second walls in a substantially vertical manner. As a result, the column cage is enclosed within a column space defined by the second walls of the tunnel forms and at least portions of the first blackouts. Second blockouts are positioned substantially horizontally in the space between the second walls such that a substantially horizontal plane is defined by the first walls of the tunnel forms and at least portions of the second blockouts. The second blockouts do not extend over the column space. Thus, the second blockouts provide continuity of the first walls of the tunnel forms in the space between the second walls of the tunnel forms.

A plurality of metal chairs can be positioned on the substantially horizontal plane, that is on the first surfaces of the tunnel forms. At least two post-tensioning cables can be draped over at least some of the metal chairs such that the cable is supported by the metal chairs and such that the cable extends directly over the column space. In addition, reinforcements, such as rebar, can be placed over at least some of the metal chairs.

Next, concrete can be poured on the substantially horizontal plane and within the column space so as to substantially simultaneously form a substantially horizontal slab and a substantially vertical column. The concrete can be allowed to sufficiently cure, such as per the design specification. Then, the tunnel forms can be removed. The underside of the horizontal slab can be supported with shoring. Further, the at least two cables can be tensioned. Thus, the cables provide support as a flat beam in the horizontal slab so that the columns can be used and largely spanned apart.

In another respect, aspects of the invention include a method of forming a concrete column that is offset from a row of columns. At the outset, there is a first substantially horizontal concrete slab. A pair of tunnel forms are provided. Each tunnel form having a first wall and a second wall extending substantially perpendicularly therefrom. The tunnel forms are erected on top of the first slab such that the second walls of the tunnel forms are substantially vertically oriented and opposingly spaced apart and such that a substantially horizontal plane is defined by the first walls of the tunnel forms. A first blockout is placed on the first wall of one of the tunnel forms. Thus, the first blockout is provided in the desired location of a secondary poured column.

Substantially horizontal reinforcements are provided on top of the substantially horizontal plane proximate the first blockout. Substantially vertical reinforcements are provided on top of the substantially horizontal plane. The substantially vertical reinforcements extend in a substantially linear path from at least one side of the first blockout. Concrete is then poured on top of the substantially horizontal plane so as to form a substantially horizontal second slab.

After the concrete sufficiently cures, then the tunnel forms as well as the first blockout can be removed. The second slab will have an opening where the first blockout was positioned. The underside of the second slab can be supported with shoring after the tunnel forms are removed, preferably shoring is provided after the removal of each tunnel form.

A column cage can be attached to a dowel set provided on the first slab such that the column cage extends substantially vertically upward therefrom and through the slab opening. A plurality of vertical forms can be provided between the first and second slabs so as to enclose the column cage in a column space therebetween. The column space can be directly beneath and can substantially correspond to the slab opening. At least two opposing substantially vertical forms can be provided on top of the second slab to define a upturn beam space. The substantially vertical reinforcements extending from the second slab can be disposed in the beam space between the forms.

Concrete can be poured into the column space and the beam space so as to substantially simultaneously form a concrete column, an upturn beam, and a portion of the second slab. The column extends between and engages the first and the second slabs. The upturn beam can structurally tie the offset concrete column to the second slab.

Embodiments also relate to various mid to high rise concrete structures. For instance, in one case, the structure includes a first substantially horizontal concrete slab and a second substantially horizontal concrete slab. The first slab has a plurality of concrete curbs extending substantially vertically upward therefrom. The second slab is located above the first slab. The structure includes a plurality of substantially vertical concrete columns. The columns can be at least about 8 inches wide in any direction. In one embodiment, the columns can be substantially rectangular. Each column extends between and engages the second slab and one of the concrete curbs. The columns and the second slab can be monolithic. The columns are substantially aligned in a row.

At least two post-tensioned cables can extend through the second slab so as to extend over each of the columns. The cables can provide support as a flat beam between the concrete columns. Anchors can be provided near each end of the second slab. The anchors hold the at least two cables in tension. The cables can span in substantially one direction. Thus, the cables provide substantially unidirectional support as a flat beam to the second slab such that the second slab is one way reinforced. The cables can extend through the second slab in a substantially undulating manner.

The structure can further include reinforcements in the second slab. At least some of the reinforcements can extend over the concrete columns. The reinforcements can extend through the second slab in substantially the same direction as the cables. Alternatively, the reinforcements extend through the second slab so as to be substantially transverse to the cables.

Embodiments of the invention are also direction to mid to high rise concrete structures with a column that is offset from a row of columns. The structure includes a first substantially horizontal concrete slab. The first slab has a plurality of concrete curbs extending substantially vertically upward therefrom. The structure also includes a second substantially horizontal concrete slab. The second slab is located above the first slab.

The structure includes a plurality of substantially vertical concrete columns. Each column extends between and engages the second slab and one of the concrete curbs. The columns are substantially aligned in a row. One or more columns are offset from the row of concrete columns. At least two post-tensioned cables extend through the second slab so that the cables extend over each of the columns and substantially proximate to the offset column. The cables can act as a flat beam between the concrete columns. In one embodiment, the cables span in substantially one direction. In such case, the cables can provide substantially unidirectional support to the second slab; thus, the second slab can be one way reinforced. The cables can extend through the second slab in a substantially undulating manner.

An upturn beam extends substantially vertically upward from the second slab. The upturn beam is structurally connected to the second slab, such as by a plurality of stirrups extending up from the second slab and into the upturn beam. The upturn beam, the offset column and a portion of the second slab are monolithic. Thus, punching shear due to the cold joint around the offset column is substantially prevented.

The structure can include a substantially vertical concrete support (column or wall) extending between and engaging the second slab and a curb on the first slab. The vertical support can be monolithic with a portion of the second slab and the upturn beam. The upturn beam extends on top of the second slab, spanning between the vertical support and the offset column. The vertical support can be substantially parallel to the row of columns. The upturn beam can be substantially perpendicular to at least one of the vertical support and the row of columns. Anchors can be provided near each end of the second slab. In one embodiment, the anchors can be disposed within the second slab. The anchors can hold the at least two cables in tension.

The structure can further include reinforcements in the second slab. At least some of the reinforcements can extend over the concrete column. The reinforcements can extend through the second slab in substantially the same direction as the cables and/or so as to be substantially transverse to the cables.

In another respect, aspects of the invention relate to a concrete structure with a cantilevered slab. The structure includes a first substantially horizontal concrete slab, a second substantially horizontal concrete slab, and a plurality of substantially vertical concrete columns. The first slab has a plurality of concrete curbs extending substantially vertically upward therefrom. The second slab is located above the first slab. Each of the columns extend between and engaging the second slab and one of the concrete curbs. In one embodiment, the columns and the second slab can be monolithic. The columns are substantially aligned in a row. The row of columns includes a first end column and a second end column. A portion of the second slab extends cantilevered beyond at least one of the end columns. The length of the cantilevered portion of the second slab can be at least about 8 feet.

At least two post-tensioned cables extend through the second slab, including the cantilevered portion, so as to extend over each of the columns. The cables act as a flat beam over the row of columns to support the cantilevered slab. The cables can extend through the second slab in a substantially undulating manner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a side elevational view of full tunnel form.

FIG. 1B is a side elevational view of a half tunnel form.

FIG. 2 is a side elevational view of a construction system and method according to aspects of the invention, showing tunnel forms arranged to form walls and/or slabs.

FIG. 3 is a top plan view of a concrete column construction system and method according to aspects of the invention.

FIG. 4 is a side elevational view of a concrete structure and construction method according to aspects of the invention.

FIG. 5 is a side elevational view of a concrete structure and construction method according to aspects of the invention.

FIG. 6 is a top plan view of a concrete structure and construction method according to aspects of the invention, showing one possible arrangement of reinforcements in the horizontal slab.

FIG. 7 is a top plan view of a concrete structure according to aspects of the invention.

FIG. 8 is a close-up top plan view of a concrete structure having an offset column according to aspects of the invention.

FIG. 9A is a side elevational view of a concrete structure and construction method according to aspects of the invention, prior to the first concrete pour.

FIG. 9B is a side elevational view of a concrete structure and construction method according to aspects of the invention, after the first concrete pour but before the second pour.

FIG. 9C is a side elevational view of a concrete structure and construction method according to aspects of the invention, after the second concrete pour.

FIG. 10 is a cross-sectional view through an upturn beam according to aspects of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Aspects of the invention address many of the shortcomings associated with prior construction systems and methods using tunnel forms. More particularly, aspects of the invention can expand the construction applications in which tunnel forms can be used and providing greater architectural design freedom. These aspects and other aspects will be discussed in connection with various tunnel form construction systems and methods. While aspects of the invention can be used in the construction of any building, the efficiency and economic benefits of the invention are especially realized in the construction of multi-story buildings, such as buildings having at least four floors. The detailed description of the invention is intended only as exemplary. Embodiments according to aspects of the invention are shown in FIGS. 2-10, but the present invention is not limited to the illustrated structure or application.

Embodiments of the invention relate to concrete structures and various methods of making such structures using tunnel forms, such as Outinord tunnel forms. Tunnel forms are known; examples of tunnel forms are disclosed in U.S. Pat. Nos. 3,979,919; 4,439,064; 4,261,542; and 6,619,885, which are incorporated herein by reference. Referring to FIGS. 1A and 1B, there are various types of tunnel forms including half tunnels 10, full tunnels 12, and wall forms (not shown). It will be understood that reference herein to the tunnel form 11 embraces all tunnel form types including those listed above. Naturally, the tunnel forms 11 can be used in various combinations for the construction project at hand. For purposes herein, it should be noted that each tunnel form 11 can have at least a first wall 14 and a second wall 16 that is substantially perpendicular to the first wall 14. Thus, when the tunnel form 11 is erected, the first wall 14 can be substantially horizontal, and the second wall 16 can be substantially vertical.

Aspects of the invention relate to a method and/or system for using tunnel forms in such a way to retain its existing benefits of tunnel form construction while expanding the range of building types in which tunnel form construction can be applied. Aspects of the invention will be described in the following construction system and method. One skilled in the art will appreciate how such a system and method will retain the benefits of tunnel form construction and how aspects of the invention can be applied to almost any building construction. It should be noted that the system and method described below are merely examples and not every step need occur or occur in the exact sequence or manner described. Similarly, not every component described below must be used.

At the outset, a substantially horizontal concrete foundation or first slab 20 can be formed. The slab 20 can provide a series of concrete curbs 22, which may or may not be monolithic with the slab 20. Multiple dowels 24 can extend substantially vertically upward from the slab 20 or columns below the floor to be constructed. Next, a column cage 26 can be positioned around the dowels 24 and can be tied to the dowels 24. The columns cages 26 can provide a general form of the column and can include vertical reinforcements as well as stirrups. Similarly, preparations can be made for any adjacent concrete tunnel walls that preferably have the same thickness of the concrete columns according to aspects of the invention.

Tunnel forms 11 can be erected such that the second walls 16 are opposingly spaced apart according to the design width of the concrete column. Further, a substantially horizontal plane can be defined by at least the first surfaces 14 of the tunnel forms 11. The tunnel forms 11 can enclose the column cages 26 on two sides. The second walls 16 of the tunnels forms 11 can be spaced from the column cage 26. When forming columns, one or more blockouts 28 can be positioned in the space between the second walls 16. A column space 30 can be formed between the opposing second walls 16 of the tunnel forms 11 and portions of the blockouts 28 v. Further, a portions of the blockouts 28 h can be disposed so as be substantially flat with the tops of the adjacent slab forming surface or first walls 14 of the tunnel forms 11. Ideally, the blockouts 28 h do not extend over the column space 30. The number of bays to be erected can depend on the amount of forms available.

Next, as shown in FIG. 4, a plurality of metal chairs 32 can be positioned on the first surface 14 of the tunnel forms 11. The metal chairs 32 can be positioned to support reinforcement materials such as rebar. The metal chairs 32 can have a variety of heights as required by the coverage design specifications. Once the metal chairs 32 and/or support bars are positioned, one way top and bottom reinforcement materials 34 t, 34 b (collectively referred to as 34), such as rebar, can be positioned on the metal chairs 32 and/or support bars such that the metal chairs 32 and/or support bars support the reinforcement materials 34. Additional top and bottom reinforcements 34 t, 34 b to the slab reinforcement can be provided above the column line 36 and perpendicular to the post-tensioning line, as illustrated in FIG. 5. Shear heads (not shown) can be erected around the columns where and if required by the design for punching shear.

Aspects of the invention further use principles of post-tensioning as a flat beam with a large span between the columns to provide support for the one-way slab. Next, additional metal chairs 32 can be arranged to provide the desired longitudinal profile of the post-tensioning cables 40 between the concrete columns 42. Per the design specification, the height of the chairs 32 can vary along the length of the cables 40 in order to create the required profile by the design, as shown in FIG. 4. For example, in one embodiment, it may be desirable for the cables 40 have a wave or undulating shape.

The cables 40 can be fixed at one end using a dead anchor 44 as is known in the art. At their other end, the cables 40 can be routed through a stress anchor 46, which is also known in the art. The cables 40 can run generally in the same direction of the walls or generally in the same direction as the row 36 of columns 42; when tightened, the cables 40 can run substantially parallel to the walls or to a line 36 formed by the columns 42. Substantially parallel include true parallel and deviations therefrom. In one embodiment, the cables 40 only extend in substantially one direction.

Top and bottom reinforcements 34 t, 34 b, such as rebar, can be erected between the columns and parallel to the post-tension cables as a part of the flat beam design, as shown in FIG. 4. Such additional reinforcement can be tied to the metal chairs 32. As shown in FIG. 6, additional top and bottom reinforcements 34 can be located over the columns 42 and perpendicular to the cables 40 at the column strip and as per the design specifications.

After all the reinforcements and the post tensioning cables 40 are positioned as desired, including all the other non-structural components such as plumbing stacks and electrical wiring (not shown), this portion of a second horizontal slab 50 including the columns 42 and any walls 43 can be poured substantially simultaneously. It should be noted that additional forms, such as edge form 13 (FIG. 2), may be used to confine the concrete within an area on top of the first walls 14 of the tunnel forms 11. Because of the efficiency of the tunnel form construction system, the pour can occur on the same day that the tunnel forms 11 are erected. In one embodiment, the thickness of the walls 43 are preferred to be equal to the thickness of the columns 42.

The strength of the concrete can be selected as required by the design. A higher strength of concrete can be used in order to achieve the minimum concrete strength for stripping the form on the next day. Also, the concrete used in the pour can be preheated over night to accelerate the curing process. Once the concrete cures to the minimum acceptable level, sometimes by the next day, the tunnel forms 11 can be removed or stripped and moved on to the next bays to be constructed. Prior to removal of the tunnel forms 11, the existing strength of the concrete can be checked to ascertain that the concrete is at the minimum strength level.

It should be noted that a column 42 formed according to aspects of the invention can be at least about 8 inches thick in any direction. Columns 42 formed in accordance with aspects of the invention can be substantially rectangular or substantially square in cross section. Further, columns 42 according to aspects of the invention can be defined by American Concrete Institute specification no. ACI-318, which is incorporated herein by reference.

The cables 40 in the flat beams 51 can be tensioned at any time after the slab reaches the required minimum design concrete strength for stressing. The tensioning of the cables 40, known as post-tensioning, provides support as a flat beam in the slab 50 so that the columns 42 can be used and largely spanned apart. The cables 40 can be fixed at one end by an dead anchor 44. At the other end can be a stress anchor 46, which can allow one way travel of the cables 40. Thus, the cables 40 can be pulled from one end or two ends, through the stress anchor 46 until the desired tension is reached. At that point, the excess cable 40 extending past the stress anchor 46 can be cut off and sealed as per specification. Again, aspects of the invention relate to a post-tensioned flat beam in which the tensioned cables 40 between the concrete columns 42 erected in the tunnel wall forms 11.

When stripping the tunnel forms 11, it is preferred if only half of a form 11 (in the case of half forms) of any bay is stripped. When one half is stripped, shoring 52 can be immediately placed at mid-span under the slab 50 to provide support to the slab 50 as per the shoring design. Additional shoring 52 can be placed under any post-tensioning flat beams in which the cables 40 between the columns 42 have not been stressed. Once the shoring 52 is in place, the second half of the tunnel form 11 can be stripped and additional shoring 52 can be placed under this portion of this slab 50 and/or the post-tensioning flat beam 51 in the slab 50. Shoring and reshoring under the post-tensioning flat beam 51 can be designed not only to support the weight of slab 50, but also any pours of slabs above since at this stage of the pour of the fresh concrete the tunnel form 11 directs the load to the line 36 of columns 42 or wall 43.

The stripped tunnel forms 11 can be moved to the next bays to be constructed. The system and method according to aspects of the invention can similarly be applied to other bays as described above. The above process can be repeated for adjacent units on the same floor or they can be applied to units above so as to form a multi-level building. The time and cost benefits of the invention are especially appreciated in buildings that are five or more stories.

Embodiments of the invention can be used to provide large cantilevered portions 58 of the second slab 50, which can be used as a balcony or a walkway, as shown in FIG. 4. Such portions 58 can be provided by using a cantilever post-tensioned flat beam formed over the concrete columns or walls. The cantilevered portion 58 can extend, for example, from about 8 to about 9 feet, beyond the end of a wall or beyond the last column 42L in a row of columns 36.

As noted earlier, the columns can be generally formed in line with each other. However, aspects of the invention can accommodate circumstances where one or more columns 60 are not in line with the other columns, such as being offset to the left or the right of the line 36 of columns 42. In other words, aspects of the invention can further relate to providing secondary columns or walls to be poured outside of the tunnel walls. One example of an offset column 60 is shown in FIG. 7. The offset or displaced column 60 may be required or desired due to any of a number of reasons such as architectural limitations or preferences. Aspects of the invention further relate to a system and/or method for providing such offset columns 60 without substantially impeding or interrupting the overall tunnel forming process.

In such cases, block-outs 62 can be provided the first surface 14 of at least one of the tunnel forms 11 prior to the first pour such that after the first concrete pour, an opening 64 will remain in the slab 50 at that location, as shown in FIGS. 9A and 9B. In addition, stirrups 66 or other reinforcements can be provided extending substantially vertically upward from the slab 50 for a future upturn beam.

To form the secondary column, reinforcement cages 26 of the secondary column can be inserted into at least one of the openings 64 and tied to the dowels from a column, foundation or curb below. Also, reinforcements 67 for the upturn beam can be erected. The secondary column 60 and upturn beam 61 can be formed by wood or metal forms 68. In the case of the column 60, the forms 68 can be substantially vertically oriented and can be placed beneath the opening remaining in the slab 50 after the first pour. The forms 68 can enclose the column cage 26 in a column space 70 therebetween. The column space 70 can be directly beneath and substantially correspond to the slab opening 64. Forms 68 can be placed on top of the slab 50 to define at least a portion of the upturn beam 51. The substantially vertical reinforcements 66 extending from the second slab 50 are disposed in the beam space between the forms.

The secondary concrete columns 60 and upturn beams 61 can be poured substantially simultaneously in order to prevent punching shear of the slab 50 at the offset columns 60. In a secondary pour, the upturn beam 51 must be poured substantially simultaneously with any secondary poured columns or column and part of a wall 43 that was blocked out for the secondary pour. The secondary concrete columns 60, upturn beam 51 and portion of the wall 43 can be formed and poured at the time where there are no tunnel forms 11 in the way. This upturn beam 61 can in general be located in a future non-bearing wall. From an architectural standpoint, intrusion of the upturn beam into an above unit is not a problem since it can be coordinated with the architect to be located in a non-bearing wall location. The upturn beam 61 can substantially minimize the potential of punching shear of the first poured slab 50 at the secondary poured columns 60 due to cold joint around the secondary columns 60. The upturn beam 61 overlaps at least a portion of the secondary column 60 or wall 43 and can extend on the slab 50 in almost any manner relative to the secondary column 60 or wall 43. The stirrups 66 can tie the upturn beam 61 to the slab 50, and the stirrups 66 can further tie the slab 50 to the secondary columns 60.

It will of course be understood that the invention is not limited to the specific details described herein, which are given by way of example only, and that various modifications and alterations are possible within the scope of the invention. 

1. A method of forming a concrete column comprising the steps of: attaching a column cage to a dowel set such that the column cage extends substantially vertically upward therefrom; providing a pair of tunnel forms, each tunnel form having a first wall and a second wall extending substantially perpendicularly therefrom; erecting the tunnel forms such that the second walls of the tunnel forms are substantially vertically oriented and opposingly spaced apart, wherein the column cage is disposed between the second walls; positioning first blockouts substantially vertically in the space between the second walls such that the column cage is enclosed within a column space defined by the second walls of the tunnel forms and portions of the first blackouts; positioning second blockouts substantially horizontally in the space between the second walls such that a substantially horizontal plane is defined by the first walls of the tunnel forms and portions of the second blockouts, wherein the second blockouts do not extend over the column space, whereby the second blockouts provide continuity of the first walls of the tunnel forms in the space between the second walls of the tunnel forms; and pouring concrete on the substantially horizontal plane and within the column space so as to substantially simultaneously form a substantially horizontal slab and a substantially vertical column.
 2. The method of claim 1 further including the steps of: allowing the concrete to sufficiently cure; and removing the tunnels forms.
 3. The method of claim 2 further including the step of supporting the underside of the horizontal slab with shoring.
 4. The method of claim 1 further including the steps of: prior to the pouring step, positioning a plurality of metal chairs on the substantially horizontal plane; and laying at least two post-tensioning cables over at least some of the metal chairs such that the cable is supported by the metal chairs and such that the cable extends directly over the column space.
 5. The method of claim 4 further including the steps of: allowing the concrete to sufficiently cure; and tensioning the at least two cables, whereby the cable provides support as a flat beam in the horizontal slab so that the columns can be used and largely spanned apart.
 6. The method of claim 4 further including the step of laying reinforcements over at least some of the metal chairs.
 7. A method of forming a concrete column offset from a row of columns comprising the steps of: providing a first substantially horizontal concrete slab; providing a pair of tunnel forms, each tunnel form having a first wall and a second wall extending substantially perpendicularly therefrom; erecting the tunnel forms such that the second walls of the tunnel forms are substantially vertically oriented and opposingly spaced apart and such that a substantially horizontal plane is defined by the first walls of the tunnel forms; placing a first blockout on the first wall of one of the tunnel forms, whereby the first blockout is provided in the desired location of a secondary poured column; providing substantially horizontal reinforcements on top of the substantially horizontal plane proximate the first blockout; providing substantially vertical reinforcements on top of the substantially horizontal plane, wherein the substantially vertical reinforcements extend in a substantially linear path from at least one side of the first blockout; pouring concrete on top of the substantially horizontal plane so as to form a substantially horizontal second slab; allowing the concrete to sufficiently cure; and removing the tunnel forms and the first blockout, wherein the second slab includes an opening where the first blockout was positioned.
 8. The method of claim 7 further including the step of supporting the underside of the second slab with shoring.
 9. The method of claim 7 further including the steps of: attaching a column cage to a dowel set provided on the first slab such that the column cage extends substantially vertically upward therefrom and through the slab opening; providing a plurality of vertical forms between the first and second slabs so as to enclose the column cage in a column space therebetween, wherein the column space is directly beneath and substantially corresponds to the slab opening; providing at least two opposing substantially vertical forms on top of the second slab, wherein the substantially vertical reinforcements extending from the second slab are disposed in the beam space between the forms; pouring concrete into the column space and the beam space so as to substantially simultaneously form a concrete column, an upturn beam, and a portion of the second slab, wherein the column extends between and engages the first slab and the second slab, whereby the upturn beam structurally ties the concrete column to the second slab.
 10. A mid to high rise concrete structure comprising: a first substantially horizontal concrete slab, the first slab having a plurality of concrete curbs extending substantially vertically upward therefrom; a second substantially horizontal concrete slab, wherein the second slab is located above the first slab; a plurality of substantially vertical concrete columns, each column extending between and engaging the second slab and one of the concrete curbs, wherein the columns are substantially aligned in a row; and at least two post-tensioned cables extending through the second slab so as to extend over each of the columns, whereby the cables provide support as a flat beam between the concrete columns.
 11. The structure of claim 10 wherein the columns and the second slab are monolithic.
 12. The structure of claim 10 further including anchors near each end of the second slab, wherein the anchors hold the at least two cables in tension.
 13. The structure of claim 10 wherein the column width is at least about 8 inches in any direction.
 14. The structure of claim 10 wherein the columns are substantially rectangular.
 15. The structure of claim 10 wherein the cables span in substantially one direction, whereby the cables provide substantially unidirectional support as a flat beam to the second slab such that the second slab is one way reinforced.
 16. The structure of claim 10 further including reinforcements in the second slab, wherein at least some of the reinforcements extend over the concrete column.
 17. The structure of claim 16 wherein the reinforcements extend through the second slab in substantially the same direction as the cables, wherein at least some of the reinforcements extend over the columns.
 18. The structure of claim 16 wherein the reinforcements extend through the second slab so as to be substantially transverse to the cables, wherein at least some of the reinforcements extend over the columns.
 19. The structure of claim 10 wherein the cables extend through the second slab in a substantially undulating manner.
 20. A mid to high rise concrete structure with a column offset from a row of columns comprising: a first substantially horizontal concrete slab, the first slab having a plurality of concrete curbs extending substantially vertically upward therefrom; a second substantially horizontal concrete slab, wherein the second slab is located above the first slab; a plurality of substantially vertical concrete columns, each column extending between and engaging the second slab and one of the concrete curbs, wherein the columns are substantially aligned in a row; a column offset from the row of concrete columns, wherein the offset column extends between and engages the first and second slabs; an upturn beam extending substantially vertically upward from the second slab, the upturn beam being structurally connected to the second slab, wherein the upturn beam, the offset column and a portion of the second slab are monolithic, whereby punching shear due to the cold joint around the offset column is substantially prevented; at least two post-tensioned cables extending through the second slab so that the cables extend over each of the columns and substantially proximate to the offset column, whereby the cables act as a flat beam between the concrete columns.
 21. The structure of claim 20 wherein the upturn beam is structurally connected to the second slab by a plurality of stirrups extending up from the second slab and into the upturn beam.
 22. The structure of claim 20 further including at least one substantially vertical concrete support extending between and engaging the second slab and a curb, wherein the vertical support, a portion of the second slab and the upturn beam are monolithic, wherein the upturn beam spans between the vertical support and the offset column.
 23. The structure of claim 22 wherein the vertical support is substantially parallel to the row of columns.
 24. The structure of claim 22 wherein the upturn beam is substantially perpendicular to at least one of the vertical support and the row of columns.
 25. The structure of claim 20 further including anchors near each end of the second slab, wherein the anchors hold the at least two cables in tension.
 26. The structure of claim 20 wherein the cables span in substantially one direction, whereby the cables provide substantially unidirectional support to the second slab, whereby the second slab in one way reinforced.
 27. The structure of claim 20 further including reinforcements in the second slab, wherein at least some of the reinforcements extend over the concrete column.
 28. The structure of claim 27 wherein the reinforcements extend through the second slab in substantially the same direction as the cables.
 29. The structure of claim 27 wherein the reinforcements extend through the second slab so as to be substantially transverse to the cables.
 30. The structure of claim 20 wherein the cables extend through the second slab in a substantially undulating manner.
 31. A concrete structure with a cantilevered slab comprising: a first substantially horizontal concrete slab, the first slab having a plurality of concrete curbs extending substantially vertically upward therefrom; a second substantially horizontal concrete slab, wherein the second slab is located above the first slab; a plurality of substantially vertical concrete columns, each column extending between and engaging the second slab and one of the concrete curbs, the columns being substantially aligned in a row, wherein the row of columns includes a first end column and a second end column, wherein a portion of the second slab extends cantilevered beyond at least one of the end columns; at least two post-tensioned cables extending through the second slab including the cantilevered portion so as to extend over each of the columns, whereby the cables act as a flat beam over the row of columns to support the cantilevered slab.
 32. The structure of claim 31 wherein the columns and the second slab are monolithic.
 33. The structure of claim 31 wherein the length of the cantilevered portion of the second slab is at least about 8 feet.
 34. The structure of claim 31 wherein the cables extend through the second slab in a substantially undulating manner. 